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The U.S. Environmental Protection Agency - Region 6 asked ATSDRto review environmental data collected at the Stephenson-BennettMine Site and determine if contamination poses a public healthhazard.

The Stephenson Bennett Mine is an inactive silver mine located10 miles northeast of Las Cruces, New Mexico. Mining wastes nearthe mine contain concentrations of lead in excess of 10,000 partsper million (ppm). These wastes have washed down an arroyo intonearby residential areas.

In March - June of 1997, the EPA collected surface soil samples(0-6 inches) from residential lots and analyzed them for lead,arsenic, cadmium, and zinc. The EPA also collected house dustsamples and analyzed them for lead, arsenic, and cadmium. Theconcentrations of metals detected in 208 soil samples and 121house dust samples are listed in the table below:

Table 1.

Minimum and maximum concentrations of metals detected in soil and house dust samples (in ppm)

Soil

Dust

min

max

min

max

Lead

400

32,200

36.7

7647.1

Arsenic

15.6

860

0.2

310.2

Cadmium

0.2

83.9

0.5

73.9

Zinc

228

24,200

NA

NA

NA - not analyzed

Ambient air particulate samples were collected over an 8-hourperiod and analyzed for lead, arsenic, and cadmium. No cadmiumwas detected in the air particulates, and lead was detected in 17of 163 (10 percent) of samples at a maximum concentration of0.421 µg/m3. Arsenic was detected in air particulates at amaximum concentration of 7.57 µg/m3 and was detected in 51 of 163 (30 percent) of samples at a concentration in excess of 1 µg/m3.